The article discusses the investigation of quantum mixtures of ultracold atomic gases, which are a powerful experimental framework for studying a wide range of physical phenomena. The authors categorize these mixtures into homonuclear and heteronuclear spin mixtures, highlighting their unique features and experimental setups. They explore the physics of few-atom systems, impurity problems, and many-body physics, focusing on three-dimensional bulk mixtures of neutral atoms. The review covers the behavior of mixtures under different interaction regimes, such as Bose-Einstein condensates (BEC) and Fermi gases, and discusses the emergence of exotic states like Efimov states and polaronic systems. The article also delves into the phase diagrams and critical points of these mixtures, including the BEC-BCS crossover in Fermi-Fermi mixtures and the Stoner model for itinerant ferromagnetism in repulsive Fermi mixtures. The authors provide a comprehensive overview of recent experiments and future directions in this rapidly evolving field.The article discusses the investigation of quantum mixtures of ultracold atomic gases, which are a powerful experimental framework for studying a wide range of physical phenomena. The authors categorize these mixtures into homonuclear and heteronuclear spin mixtures, highlighting their unique features and experimental setups. They explore the physics of few-atom systems, impurity problems, and many-body physics, focusing on three-dimensional bulk mixtures of neutral atoms. The review covers the behavior of mixtures under different interaction regimes, such as Bose-Einstein condensates (BEC) and Fermi gases, and discusses the emergence of exotic states like Efimov states and polaronic systems. The article also delves into the phase diagrams and critical points of these mixtures, including the BEC-BCS crossover in Fermi-Fermi mixtures and the Stoner model for itinerant ferromagnetism in repulsive Fermi mixtures. The authors provide a comprehensive overview of recent experiments and future directions in this rapidly evolving field.